This invention relates to a split nail used when mounting a wood or other material on air bubble lightweight concrete.
When mounting wood or other material on a fragile and inflexible building material such as air bubble lightweight concrete (hereinafter referred to as ALC), since an ordinary nail does not provide a sufficient force to secure these materials to each other, it is necessary to use a split nail which exhibits high resistance to pulling forces by spreading their legs when driven in.
Examined Japanese Utility Model Publication 57-19449 proposes such a split nail coupled together at their heads. Tapered surfaces are formed at the tip portions thereof opposite to each other. A strip-shaped foldable member made of metal is sandwiched between the legs. Also, a washer is fitted around the legs near their tips. When the split nail is driven into a starting hole formed in the wood or other material and the ALC, the reactive force caused by the nail acts on the tapered surfaces of the tip portions so as to split the legs gradually. The reactive force also acts on the foldable member to compress and deform it as the legs are driven in deeper. Thus, the ALC is compressed, so that the pull-out resistance increases.
Such a split nail will spread its legs by the pressure, i.e. the reactive force applied to the tapered surfaces of the legs by hitting the nail. If the ALC is too hard, the reactive force acts on the ALC so strongly that the legs are spread apart before being driven to a sufficient depth. If it is too soft, the legs cannot be spread sufficiently due to a weak reactive force of the ALC. Thus, the degree of opening will vary depending upon the hardness of the ALC.
Also, a starting hole has to be formed in the wood because the nail cannot be directly driven into the wood. This work is bothersome.
An object of this invention is to provide a split nail which provides a constant pull-out resistance by spreading its legs at a predetermined depth regardless of the hardness of the ALC and which can be driven in without the necessity of forming a starting hole.